hello,
i am trying to repair a fault with an user interface circuit (UIC) board and control board out of an old 1987's computerized programmable Pfaff sewing machine (made in Western Germany).
a for fun project for me , a challenge :)
programming consists of storing values in memory locations using keys ( +/- buttons) on UIC board
PROBLEM : a group of 3 (+/-) *momentary switch* buttons on UIC board used to change memory values do not make any changes when pressed.
the UIC board has a VFD output display (16 chars) and 12 input buttons and 5 indicator LEDs. All but 3 of the buttons register presses correctly. the 3 broken buttons seem to be individually ok as i get continuity changes when i test with multimeter and push buttons.
this UIC board is connected to the control board via 12 conductor ribbon ???
I am not sure what kind of things to do to isolate trouble ........
i have dome visual inspection of solder joints and components with no obvious issues.
How would the VFD display values , LED indicatiors and inputing buttons be managed through a 12 conductor ribbon ??? in 1980's style ?? how to trace ot monitor value changes.
Any troubleshooting or tracing ideas advice would br greatly appreciated.
thanks, rob